Ellipsoid internal cross section waveguides were heretofore known for providing a broadband tuning capability, allowing such a waveguide to accommodate a range of frequencies without substantial power loss or reflection. These, however, have not been practically employed, other than in microwave systems. Rather, in radio frequency systems, for example below 1 GHz, the art teaches the use of circular waveguides, which have good transmission properties at a particular center frequency, including low power loss and reflection ratio, or rectangular waveguides, which accommodate a range of frequencies and have low reflection ratio, but have relatively high power loss.
Typically, such radio frequency waveguides are employed, at least in part, to communicate a high power radio frequency transmission between a base-station amplifier and the antenna. The antenna, in turn, is a tall structure raised off the ground by a tower. The waveguide in such circumstances may therefore subject to substantial wind forces, and, for example, should be able to withstand at least hurricane force winds. Due to the relatively large size of these waveguides, for example, 30-60 cm in diameter, and the large exposed distances, for example 300-500 meters, the wind force and turbulent stresses may be substantial, requiring either a protective sheath or a mechanically reinforced waveguide structure, for waveguides having the rectangular external profiles. Round waveguides, on the other hand, have acceptably low wind resistance, but must be provided in a specific diameter for each intended installation. It is known, therefore, to sheath a rectangular waveguide in a smooth encasement, to provide a dual wall structure.
The known ellipsoidal cross section radar waveguides, e.g., with a 2.84' or 1.37' major axis ID, have substantially smaller projected areas, and thus would inherently present less wind resistance per unit length compared to a rectangular waveguide. These radar waveguides are typically operated at frequencies above 2.0 GHz, and with relatively high power levels primarily in pulse mode operation. In these systems, the ellipsoidal cross section waveguide is typically employed for its advantageous electrical properties, low loss and low reflection ratio, especially when flexed. As such, external wind resistance is not a particular consideration for design and use of these systems for radar and point to point waveguide structures, and typically these waveguides are not exposed to the elements over great distances.
Chu, L. J., "Electromagnetic Waves in Elliptic Hollow Pipes of Metal", Journal of Applied Physics 9:583 (9/1938) discusses electrical performance of elliptical waveguides.
U.S. Pat. Nos. 5,171,942 and 5,418,333 provide an elliptic cross section stranded cable which damps conductor strand vibrations by canceling wind-induced forces.
U.S. Pat. No. 4,687,884 provides a low drag conductor for power transmission lines having a textured outer surface.
It is known, in the field of nautical design, to employ ellipsoidal cross section masts to reduce wind turbulence.